Static furnace for the thermal decomposition of solids at high temperatures by thermal radiation

ABSTRACT

A furnace for the thermal decomposition of solids by thermal radiation having an inlet for admitting the solids at an upper part with the solids dropping by gravity in the furnace. There is at least one heated radiator body within the furnace below the inlet to produce radiant heat energy to decompose the solids dropping in the furnace and the gases produced by the decomposition rise in the furnace to preheat the solids admitted at the inlet. The furnace also includes a heat exchanger whose liquid is heated by the decomposed solids, and there are a plurality of radiator bodies each in the form of a closed chamber with a burner to heat a plate which radiates the heat.

TECHNICAL FIELD

The present invention refers to a static furnace, more specifically to astatic furnace for the thermal decomposition of solids at hightemperatures by thermal radiation.

SUMMARY OF THE INVENTION

The furnace of the present invention is characterized by the utilizationof essentially thermal radiation as the source of the heat needed in theprocess. Hence, the direct contact with the hot gases is avoided, thesehot gases being generated in the combustion of fuels in the furnaceenvironment, also avoided is the contamination of the CO₂ or of thesulfur (vapor) formed in the thermal decomposition of the limestone orof the pyritic substances, and of the solid residue formed in thefurnace.

The source of thermal radiation can be electric energy, combustion offossil and/or renewable fuels, externally to the furnace environment andother forms of heating the furnace chamber by thermal radiation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents the front elevation of a static furnace for thethermal decomposition of solids at high temperatures by thermalradiation of the present invention.

FIG. 2 represents a back elevation of the furnace of the invention.

FIG. 3 a top view of the furnace of the invention.

FIG. 4 represents a section according to the plane A--A in FIG. 3.

FIG. 5 represents a section according to the plane B--B in FIG. 4.

DISCLOSURE OF THE INVENTION

This furnace is intended for the decomposition of solids at atemperature range from 500° C. to 1200° C., for, for instance, limestonecalcination (CaCO₃), to produce a lime (CaO) of high reactivity and purecarbonic gas (CO₂), at 100%, or the thermal decomposition of iron andcopper pyrites, such as the pyritic rejects of coal, and the pyriticconcentrates of iron and copper, to produce sulfur 100% pure and aresidue of iron sulfide of industrial application.

The thermal radiation furnace, according to the present inventioncomprises the following main parts:

a solids feeding system;

a solids pre-heating system which is also used in the cooling of theformed gases/vapors;

a reactor for the thermal decomposition by thermal radiation;

a cooling system for the solid products of the reaction and for thesolids thermal energy recovery;

a system for the discharge of the solid products; a system for theheating of the furnace to the temperatures of thermal radiation;

a system to collect the gas/vapors formed in the reaction; and

a system to recover the energy of the flue gases whenever this is thesource of energy for the thermal radiation.

Solids Feeding System

The solids are fed through the top of the furnace and are moved in theirpath by gravity action until their removal from the furnace. A feedinghopper 1, silo or other means to store the solids, in the highest partof the assembly, discharges the solids through a rotating valve 2, forexample, or other feeding mechanism to the furnace, which definestightness, preventing the gases/vapors formed in the environment toescape.

Solids Pre-Heating and Gases/Vapors Cooling System

The solids are fed to the furnace at ambient temperature and theyrequire to be heated up to the process temperature of the thermaldecomposition, in the range 500° C. to 1200° C. On the other hand, thegases/vapors formed in the thermal decomposition which occurs in thereactor by thermal radiation being in the range of temperatures between500° C. and 1200° C., must be cooled down to temperatures suitable totheir recovery and utilization in the following steps.

Therefore, the solids pre-heating takes place simultaneously to thegases/vapors cooling in the upper regions of the furnace, where thesolids descend by gravity and the gases/vapors rise in counter-flow andin direct contact with the solids, thus producing the desired effects.

Once heated to the desired temperature of operation, the solids enterthe thermal decomposition reaction zone, which is strictly maintained atthis defined temperature, rigorously controlled by the heating sourcesof those thermal radiation surfaces. The downflow in the reactor iscaused by the gravity action. The solids remain in this reaction zonethe necessary time for their complete conversion and the production ofthe desired products, that is, the residence time which is controlled bythe solids movement by gravity through a mechanism of solids motion atthe bottom of the furnace. To keep the quality or the purity of thegas/vapor formed, a slight overpressure is maintained in the furnace toprevent the contamination of the furnace atmosphere by externalgases/vapors. Three reaction zones are shown in the figures. The heat toheat up the ceramic plates 4 is provided by burners 3 located incompletely isolated chambers 5 from the reactions/reaction zones of thefurnace to avoid the contamination of the reaction products with thecombustion products of the fuel and of the excess air. The chamberwalls, where the burners are installed, are vertical and the refractoryplates will be heated up to transfer the heat received via combustion tothe solids (limestone or pyrites, pending upon the application) bythermal radiation.

The figures present four chambers and twelve burners each chamber, as anexample. The number of burners for maximum energy efficiency will bedefined as function of the flame intensity, shape and temperature.

Solid Products of the Reaction Cooling System and the Solids ThermalEnergy Recovery

After completion of the thermal decomposition reaction, the solids inthe temperature range 500° C.-1200° C. will be cooled to temperaturessuitable for their handling, discharge and/or further utilization inother process steps downstream the furnace. The heat recovery from thesolid products with their consequent cooling, can be made, for example,also by thermal radiation to a system of water cooled wall, to producehot water and/or steam. Such water wall is similar to those existing inboilers in which the tubes 6 in a vertical position, united by fins orcomposing the waterwall, are filled up with water, from a lower waterheader 8b and receiving the heat of the solid products within thefurnace, by thermal radiation quantity, the water is heated up and/orsteam is produced which is guided then to the upper hot water or steamheader 8a. In this system, the solids follow their movement downwards bythe action of gravity, allowed by a mechanism, for example, rotaryvalves 7 actuated by low energy consumption motors at the lowest part ofthe furnace or by an endless screw, which at the same time, makes thesealing and tightness of the furnace against the intake of air and/orother gases to the interior of the furnace, which would contaminate thedesired gases/vapors and/or solid products. Hence, the same heattransfer mechanism is used, that is, the thermal radiation, to supplythe heat of reaction of thermal decomposition, in the reactor, and forthe thermal energy recovery and cooling of the reaction solid products.

Another way to recover the thermal energy contained in the solids andtheir simultaneous cooling, can be to send the solids to an air tightcompartment, a silo for example, with double sealing and send air intoit, cooling the solids and heating up the air which would serve ascombustion air to the fuel burners.

Discharge of Solid Products System

Once the solids are cooled, these reaction products are discharged fromthe furnace, by gravity, through the rotary valve 7, or endless screw,to the desired site.

Heating of the Furnace to the Thermal Radiation Temperatures System

To reach the temperatures which are needed to the conduction of theprocess by thermal radiation, the external source of heat to the furnacesurfaces can be electric energy or any other, for example, the burningof fossil fuels or renewable energy, for example, in burners localizedin compartments, adequately designed, to optimize the heating process tothe walls/surfaces of the furnace. Those burners and the burningcompartments must be in a sufficient number for the desired productionrate, and their specification is a function of the temperature to bereached for the reaction process to take place. The utilization of thetemperature and the flame radiant surface of the burners must beoptimized, for the desired heating of the surfaces/walls of the furnace.

Gas Collecting/Vapor Collecting System

The gas/vapor of interest, formed in the reaction of thermaldecomposition, should be recovered under conditions of their furtherutilization. An induction blowing system, downstream the furnace,defines the needed conditions to remove that gas/vapor. Care should betaken that the gas/vapor be at a temperature above its condensation atthe exit to the furnace, or a partial condensation of one of itscomponents, or above the dew point if it is a mixture of gases/vapors.

The gas/vapor formed, after its cooling and pre-heating of the solidsbefore the reaction, enters a gas/vapor collector/header, at theuppermost part of the furnace, from where it is removed from thefurnace. The collecting system for the gas/vapors must maintain a slightoverpressure in the furnace atmosphere, to avoid its contamination withgases/vapors from outside.

Flue Gases Energy Recovery System

One of the possible external sources of heat, for heating of thesurfaces/walls of the furnace to the temperature of radiation for theprocess, is the combustion of fossil or renewable fuels, liquid, withspecially selected burners for the desired application, so that the fuelenergy use will be optimized, by means of the high temperature of theflame and of its surface, and of the temperature of the flue gases.

The burners are placed in the front part of the furnace in compartmentsspecially designed for this application, in an adequate number to reachthe temperature of the surfaces/walls of the furnace, suitable to theprocess. The flue gases are removed for example, from the rear part ofthose compartments and, might be used, in conventional equipmentsalready available in the marketplace, for the pre-heating of thenecessary air to the combustion which was itself the source of theseflue gases.

The electric energy as source of external heat could only find practicalapplication in those economic situations, in which, for example, theelectric energy is cheap or can be generated at the site at low costs,or even, close to the furnace.

The figures present the typical configuration of the thermal radiationfurnace, in which the several parts which make it, or its systems can beeasily identified. The dimensions are typical and will depend upon theprocess and its characteristics, such as: size of the solid particles,process temperature, external source of heat, nature of the formedproducts, level of the energy recovery desired, and of the nature andcharacteristics of the solid particles.

The flue gases produced in the combustion chambers are collected in achannel 9 in the furnace, and, after preheating of the combustion air,the gases are vented to the atmosphere.

What is claimed is:
 1. A furnace for the thermal decomposition of solidsby thermal radiation comprising:an inlet for admitting the solids at anupper part of said furnace, the solids dropping by gravity into areaction zone in the furnace; at least one heated radiator body withinsaid furnace below said inlet to produce radiant heat energy radiated tosaid reaction zone to decompose the solids dropping in the furnace, thegases produced by the decomposition rising in said furnace to preheatthe solids admitted at said inlet; and a heat source external of saidfurnace reaction zone producing the heat to heat said radiator body toproduce radiant heat energy.
 2. A furnace according to claim 1 furthercomprising a cooling unit below said at least one radiator body to coolthe decomposed solids.
 3. A furnace as in claim 1 further comprising asystem for collecting the gas and vapor produced by the decomposition.4. A furnace according to claim 1 wherein said at least one radiatorbody comprises a closed chamber including a burner and a ceramic plateheated by said burner serving as said heat radiator body.
 5. A furnaceas in claim 1 wherein there are a plurality of said heat radiator bodiesspaced around said furnace.
 6. A furnace according to claim 5 whereinsaid at least one radiator body comprises a closed chamber including aburner and a ceramic plate heated by said burner serving as said heatradiator body.
 7. A furnace for the thermal decomposition of solids bythermal radiation comprising:an inlet for admitting the solids at anupper part of said furnace, the solids dropping by gravity in thefurnace; at least one heated radiator body within said furnace belowsaid inlet to produce radiant heat energy to decompose the solidsdropping in the furnace, the gases produced by the decomposition risingin said furnace to preheat the solids admitted at said inlet; and acooling unit below said at least one radiator body which comprises aheat exchanger to collect the heat of the solids decomposed by thethermal radiation.
 8. A furnace as in claim 7 wherein said heatexchanger comprises a chamber including vertically extending tubes withfins, the chamber containing a liquid that is heated to produce a hotliquid or steam.
 9. A furnace for the thermal decomposition of solids bythermal radiation comprising:an inlet for admitting the solids at anupper part of said furnace, the solids dropping by gravity in thefurnace; at least one heated radiator body within said furnace belowsaid inlet to produce radiant heat energy to decompose the solidsdropping in the furnace, the gases produced by the decomposition risingin said furnace to preheat the solids admitted at said inlet whereinsaid at least one radiator body comprises a closed chamber including aburner and a ceramic plate heated by said burner serving as said heatradiator body.
 10. A furnace for the thermal decomposition of solids bythermal radiation comprising:an inlet for admitting the solids at anupper part of said furnace, the solids dropping by gravity in thefurnace; at least one heated radiator body within said furnace belowsaid inlet to produce radiant heat energy to decompose the solidsdropping in the furnace, the gases produced by the decomposition risingin said furnace to preheat the solids admitted at said inlet, whereinsaid at least one radiator body includes a plate extending substantiallyvertically in said furnace for radiating heat, the solids dropping insaid furnace passing by said plate being heated by thermal radiation.11. A furnace as in claim 10 wherein there are a plurality of said heatradiator bodies spaced apart in said furnace.
 12. A furnace as in claim10 wherein each said radiator body comprises a chamber with at least oneburner for heating said plate.